Ethereum Introduces zkAPI for Private AI Payments on Mainnet

Ethereum Launches zkAPI on Mainnet

The Ethereum Foundation (EF) and the Open Anonymity Project (OA) have launched a new system called "zkAPI" on the Ethereum mainnet, allowing users to pay for AI services and other usage-based APIs without revealing their identity information or payment IDs.

Today the EF and OA announce zkAPI---a new means for private AI

Picture this: deposit ether into a vault, sign a zk proof, get a fixed amount of private inference. Advances like these help us move past middlemen's requirements that we link our data and identities.

--- Ethereum Foundation (@ethereumfndn) October 1, 2026

In this system, the issues of account linking and prompt history tracking that have traditionally accompanied API usage are resolved, enabling privacy-conscious prepaid access.

Mechanism of Private Payments via Vault Deposits and Zero-Knowledge Proofs

The process of using zkAPI begins with depositing assets into a smart contract on Ethereum known as Vault (fund custody contract). Users can deposit supported assets such as ETH or USDC, keeping their balance as a secret "private note" on their devices.

When actually using the API, the user's device generates a zero-knowledge proof utilizing Groth16 proofs, BN254 cryptography, and the Poseidon hash function. This enables the following secure and highly anonymous processes:

Proof of Balance and Eligibility :
When making a payment, it can be proven that sufficient funds are held and that there is no double spending, while concealing which deposited funds are the source. Issuance of Temporary API Keys :
The zkAPI server verifies the zero-knowledge proof and issues a short-term valid key with a set usage limit. Separation of Payments and Requests :
While prompts (instructions) are sent directly from the user's device to the AI provider, payments are processed separately on the payment layer, ensuring that the payment side cannot know the request content, and the provider cannot identify the payment source. Prevention of Double Spending :
During payment, a nullifier (serial number) is used to prevent the illegal reuse of funds while settling from the private balance. Even if the zkAPI server goes down, users can directly withdraw their balance through the vault contract.

Expansion of Applications and Limitations in Privacy

The concept of zkAPI was concretized based on a proposal originally presented by Ethereum researcher Davide Crapis and co-founder Vitalik Buterin on a forum.

The immediate focus is on AI inference handling highly confidential prompts, but due to the nature of the infrastructure, future expansions into diverse use cases such as blockchain RPC (Remote Procedure Call), image and video generation, VPN bandwidth usage, and M2M (Machine to Machine) payments are anticipated.

On the other hand, this system only protects the "payment-related links" and does not guarantee complete anonymization of all network and content information. AI providers can still recognize the content of the sent prompts and network metadata such as IP addresses, and there is a risk that sessions may be linked through repeatedly used personal information or stylistic patterns. Therefore, for those seeking stronger confidentiality, it is recommended to use routing technologies such as Tor (The Onion Router, an anonymization system for internet communications and the software that implements it).